As a power combiner, there has been known a power combiner in which Wilkinson-type couplers, directional couplers, hybrid couplers or the like are connected in multi-stages or a power combiner which uses radial lines and a power combiner which uses conical lines. When the power combiner is used by setting an input end as an output end and the output end as the input end, the power combiner functions as a power divider and hence, hereinafter, both “power combiner” and “power divider” are referred to as “power combiner/divider”.
For example, patent literature 1 discloses a power combiner/divider which uses radial lines as a power combiner/divider used for large power. The power combiner/divider disclosed in patent literature 1 which uses the radial lines is explained in conjunction with FIG. 4. FIG. 4 is a view showing the schematic constitution of the power combiner/divider of the prior art which uses radial lines (a view showing the schematic constitution of the power combiner/divider described in patent literature 1).
As shown in the drawing, the power combiner/divider 100 includes a circular box-shaped case 104 which is formed of a top plate 104a having a circular shape as viewed in a plan view, a bottom plate 104b which faces the top plate 104a in an opposed manner, and a side plate 104c which covers outer peripheries of the top plate 104a and the bottom plate 104b. A center coaxial connector (center coaxial terminal) 101a is formed on a center portion of the top plate 104a, and a plurality of peripheral coaxial connectors (peripheral coaxial terminals) 101b are formed on an outer peripheral portion of the top plate 104a equidistantly. A conversion element (coaxial line) 102a which extends to the bottom plate 104b in the inside of the case 104 is connected to the center coaxial connector 101a. A conversion element (coaxial line) 102b which extends to the bottom plate 104b in the inside of the case 104 is connected to each peripheral coaxial connector 101b. A gap portion which is formed by the top plate 104a, the bottom plate 104b and the side plate 104c constituting the case 104 forms a radial line 103.
Further, the power combiner/divider 100 is configured to function as a power combiner when the center coaxial connector 101a is used as an output terminal and the peripheral coaxial connectors 101b are used as input terminals, and is configured to function as a power divider when the center coaxial connector 101a is used as the input terminal and the peripheral coaxial connectors 101b are used as the output terminals. When the power combiner/divider 100 functions as the power divider, for example, the power combiner/divider 100 is operated as follows. To be more specific, an incident wave from the center coaxial connector 101a is converted into a radial line mode from a coaxial TEM mode by the center conversion element 102a. A wave which is converted into a radial line mode propagates concentrically toward the outside from the center, and the wave is converted into the coaxial TEM mode from the radial line mode in the same manner by the peripheral conversion elements 102b, and is outputted to the respective peripheral coaxial connectors 101b at the same phase and equal amplitude.
Impedance Z of the radial line 103 of the power combiner/divider 100 is set, as expressed by the following formula (formula 1), proportional to a height of radial line 103, inversely proportional to a distance R from a center portion of the radial line 103. Assuming the number of combining (or the number of dividing) as N and impedance of the coaxial connector 101a, 101b as Z0 in the power combiner/divider 100, impedance Z of the radial line 103 is expressed by the following formula (formula 2).Z=√(μ/ε)×H/(2πR)=η×H/(2πR)  (formula 1)    H: height of radial line    η: natural impedance of medium (377Ω in this case)    R: distance from the center of radial lineZ=Z0/N  (formula 2)
Further, for example, non-patent literature 1 is disclosed a power combiner/divider which uses a conical line as a power combiner/divider used for large power.
The schematic constitution of the power combiner/divider disclosed in non-patent literature 1 which uses a conical line is explained in conjunction with FIG. 5. FIG. 5 is a view showing the schematic constitution of the power combiner/divider of the prior art which uses the conical, line (view showing the schematic constitution of the power combiner/divider disclosed in non-patent literature 1).
As shown in the drawing, the power combiner/divider 200 includes a body portion 204 having a circular shape as viewed in a plan view, and a center coaxial connector 201a which is formed on a center portion on one surface of the body portion 204. A plurality of peripheral coaxial connectors 201b are formed on an outer peripheral portion of the other surface of the body portion 204. A coaxial line 202a which extends to the inside of the body portion 204 is connected to the center coaxial connector 201a. Coaxial lines 202b which extend to the inside of the body portion 204 are connected to the peripheral coaxial connectors 201b. A gap portion indicated by symbol 203 in the drawing forms a conical line. In this power combiner/divider 200, the coaxial line 202a constitutes “¼ wavelength impedance converter”, wherein “D1” in the drawing indicates an inner diameter of a coaxial line outer conductor, and “D2” in the drawing indicates an outer diameter of a coaxial line inner conductor.
Characteristic impedance (Z10) of the coaxial line 202a is set so as to satisfy the relationship expressed by the following formula 3 between the inner diameter (D1) of the coaxial line outer conductor and the outer diameter (D2) of the coaxial line inner conductor. Accordingly, the characteristic impedance (Z10) of the coaxial line 202a can be obtained based on the inner diameter (D1) of the coaxial line outer conductor and the outer diameter (D2) of the coaxial line inner conductor using the following formula 3.Z10=60lnD1/D2  (formula 3)